A 7 year old, 7 month pregnant, Limousin-Simmental cross cow presented to the Cornell University Equine and Farm Animal Hospital for evaluation of anorexia of three weeks duration. The cow had been unresponsive to antibiotics and a change in feed as prescribed by the referring veterinarian. On presentation, the cow's initial problem list included depression, fever, tachycardia, loose manure, decreased intestinal motility, ketonuria, sensitivity to cranial abdominal palpation, and a distended abdomen with a fluid wave on ballottement. The cow was treated symptomatically, and further diagnostics including complete blood count, chemistry panel, serial abdominal ultrasounds, abdominocentesis and a liver biopsy were performed. With progressive abdominal distention, a therapeutic abdominocentesis was performed and produced 140 L of peritoneal effusion. With differential diagnoses including gastrointestinal neoplasia, hepatic neoplasia, and portal hypertension, a poor prognosis was indicated and her owners elected euthanasia. On necropsy, signet ring adenocarcinoma was identified in the distal jejunum, with metastasis to mesenteric lymph nodes, carcinomatosis throughout the peritoneal cavity, and neoplastic thromboembolism of the liver. To the author's knowledge, this is the first documented case of the signet ring subtype of intestinal adenocarcinoma in a cow.